The quantitative determination of analytes in body fluids is of great importance in the diagnoses and maintenance of certain physiological abnormalities. For example, lactate, cholesterol and bilirubin should be monitored in certain individuals. In particular, determining glucose in body fluids is important to diabetic individuals who must frequently check the glucose level in their body fluids to regulate the glucose intake in their diets. The results of such tests can be used to determine what, if any, insulin or other medication needs to be administered.
Determining the analyte concentration of, for example, glucose is typically performed by invasive methods. It would be desirable to determine analyte concentrations by using a non-invasive method.
Non-invasive methods may incorporate the use of different types of signals to determine the analyte concentration. One type of signal is a Raman spectral signal. The use of Raman spectral information, however, has had limited application in determining non-invasive analyte concentrations because the signals tend to be very weak. There a number of factors that contribute to the very weak Raman signal collected from the skin. One factor is the limited amount of high-intensity energy that one can safely deliver into tissue without causing photo-damage to the tissue. A second factor is the limited Raman scattering efficiency inherent to most molecules of analytical and physiological interest. A third factor is the scattering and absorbance characteristics of the tissue that limit the amount of energy that can be effectively delivered into the tissue and the amount of Raman spectral information that can be collected from the tissue.
Another type of signal is a fluorescence signal, which like Raman signals also has disadvantages. Fluorescence signals are more general in nature than Raman signals. Fluorescence molecules of interest may be of a smaller number than desired. The scattering and absorbance characteristics of the tissue limit the amount of energy that can be effectively delivered into the tissue and the amount of fluorescence spectral information that can be collected from the tissue.
Optical absorbance and tissue scattering, which are two fundamental optical properties of tissue, can be transient during non-invasive detection of an analyte such as glucose. Optical absorbance and tissue scattering can affect the glucose concentration measurement.
It would be desirable to develop a non-invasive method using spectral information such as Raman or fluorescence spectral information that more accurately determines the analyte concentration.